The present disclosure relates to a device for measuring the hydraulic conductivity of porous materials in situ, and more particularly relates to a permeameter probe for use with borehole infiltration, the probe measuring the hydraulic conductivity of soil.
When preparing to use land for agricultural, mining, or other developmental purposes, it is often necessary to obtain measurements of the hydraulic conductivity of soil. Hydraulic conductivity values provide a basis for safe and economical land use. These measurements are important considerations in design and construction of building and roadway structures and are central to planning for waste water applications, irrigation systems, mining operations, and many other systems. Further, the measurements may be necessary in and of themselves to comply with local ordinances and/or federal regulations.
Approximation of soil hydraulic conductivity at a particular location using available methods is both challenging and expensive, often requiring multiple measurements over a period of several days in order to obtain reliable results. For many applications, the soil hydraulic conductivity must be measured in situ, rather than by measurement of a sample. This is because the very removal of the sample from the targeted location changes the conditions of the sample.
One system and method for measuring soil hydraulic conductivity prescribed by the prior art uses borehole infiltration with a permeameter probe. Publication ASTM D6391-11, the entirety of which is incorporated herein by reference, sets forth exemplary standards for borehole testing. FIG. 1 is a depiction of a prior art permeameter probe 100, wherein a casing 120 is placed at the bottom of borehole 110. An annular sealant 125 is placed around the bottom of the casing 120 along the bottom of the borehole 110 to ensure a predictable measurement. A secondary sealant 126 is also placed around the periphery of the casing 120, between the casing 120 and the walls of the borehole 110, to support the shape of the casing 120 and the integrity of the borehole 110. A cap 130 is located on the top of the casing 120. The cap 130 includes a vertically protruding nozzle 140 that attaches to a standpipe 150. A first coupling 135 attaches the cap 130 to the casing 120 and a second coupling 145 attaches the nozzle 140 to the standpipe 150. In this example, where the prior art permeameter probe 100 comprises a constant-head arrangement, the standpipe 150 further includes a top cap 160, enclosing the top of the standpipe 150, with a third coupling 155 attaching the top cap 160 to the top of the standpipe 150. The permeameter probe 100 further comprises a rubber stopper 170 for enclosing the standpipe 150, and a compression fitting 175, through which is inserted a mariotte tube 180. A scale 190 is also provided to measure the amount of water that has been absorbed by the soil over a period of time.
Because in situ measurements are often demanded, due to the relative simplicity and general acceptance in the field, the constant-head permeameter probe 100 described above remains a commonly used solution. This and other prior art devices, however, suffer from various issues, such as frequent leakage from the various couplings and lengthy setup times.